Environmental contamination of Hg(II) and Pb(II) can result in poisoning and death [(a) Sherif A. et al., Trends in Analytical Chemistry, 2012, 38, 98. (b) Cheng Z. et al., Foland, Appl. Geochem, 2005, 20, 353] or severe damage to the brain [Mason R. P., et al., Water Air Soil Pollut., 1995, 80, 915], kidneys, nervous system, and red blood cells [Toplan S., et al., J. Trace Elements Med. Biol., 2004, 18, 179]. Governments throughout the world are continuing to tighten contaminant concentration limits and guidelines of heavy metals ((HMs) for industrial and environmental waters. Additionally, the World Health Organization recommends the standard allowance for water quality to be less than 10 ppb for Pb, Cd, Hg, and other toxic metal ions. Despite the increasing demands for simple and rapid monitoring of HMs in water, the sensitivities of commercial methods are insufficient to meet the recommended concentration guidelines [Nora Savage et al., (eds.), Nanotechnology Applications for Clean Water, 2009, 417-425. William Andrew Inc].
There are urgent needs for simple, inexpensive, sensitive and selective detection of metal ions for a wide range of applications including industrial process management, chemical threat detection, medical diagnostics, food quality control and environmental monitoring. The use of simple, inexpensive, rapid responsive and portable sensors would allow large scale monitoring of heavy metals [(a) Sherif A. et al., Microporous and Mesoporous Materials 2013, 166, 195-205 (b) Miyawaki A., et al., Nature 1997, 388, 882; (a) Sherif A. et al., Talanta 2012, 98, 69-78 (b) Oehme, I., et al., Mikrochim. Acta, 1997, 126, 177; (a) El-Safty S. A., et al., Sensors and Actuators B, 2013, 176, 1015, (b) Buhlmann P. et al., Chem. Rev., 1998, 98, 1593, (a) Shenashen M. A. et al., Journal of Hazardous Materials, 2013, 244-245, 726, (b) Keith, L. H. et al., Chem. Rev., 2007, 107, 2695; (a) El-Safty S. A. et al., Talanta 2011, 83, 1341-1351 (b) Sherif A. et al., Sensors and Actuators B 2012, 166-167, 253-263 (c) Spichiger-Keller U. S., Chemical sensors and biosensors for medical and biological applications. Wiley-VCH, 1998, Weinheim, Germany]. In comparison with other spectroscopic methods, the use of a colorimetric detection method is simple and eliminates the need for sophisticated instruments since results can be detected by “naked-eye”.
The determination of HMs in the aquatic environment is of tremendous interest due to their hazardous effects on the ecosystem and ultimately human health. Chemical sensor technologies that specifically detect cations or anions are based on chemical recognition of HMs and subsequent transduction of the analytical signal. Colorimetric sensors are based upon detection of an analyte-induced color change in the sensor materials [Gunnlaugsson T. et al., Org. Lett. 2004, 6(10), 1557; Martinez R. et al., Org. Lett. 2005, 7(26), 5869; Oehme I. et al., Microchim. Acta 1997, 126(3), 177]. Colorimetric sensing systems allow sensitive and simple signal detection while eliminating the need for sophisticated equipment or well-controlled environments. Sensing responses in terms of sensitivity, selectivity, and fast response-time of the chemosensors are induced by the immobilized indicator chromogen “molecular probe”—analyte “cation” interactions [(a) El-Safty S. A., et al., Sensors and Actuators B, 2013, 176, 1015, (b) Buhlmann P. et al., Chem. Rev., 1998, 98, 1593]. These binding events transduce signaling responses that have posed considerable constraints based on the chemosensor design. Recently, the ability to manipulate chromophore probes into nanoscale materials as sensing receptors has received attention in the design of flexible chemosensors for recognition of several species such as metal cations [(a) Wirnsberger G. et al., Chem. Commun. 2001, 119; (b) Nicole L. et al., Chem. Commun. 2004, 2312; (a) Balaji T. et al., Angew. Chem. Int. Ed. 2006, 45, 7202; (b) El-Safty S. A. et al., Chem. Eur. J. 2007, 13, 9245; (c) El-Safty S. A. et al., Adv. Func. Mater. 2007, 17, 3731; (d) El-Safty S. A. et al., Phys. Chem. C 2008, 112, 4825; (e) El-Safty S. A. et al., Chem Mater 2008, 20, 2644; (f) El-Safty S. A. et al., Adsorption 2009, 15, 227] as well as charged and neutral organic molecules [(a) Comes M. et al., Adv. Mater. 2004, 16, 1783; (b) Desacalzo A. B. et al., J. Am. Chem. Soc. 2005, 127, 184; (c) Balaji T. et al., Analyst 2005, 130, 1162; (d) Metivier R. et al., J. Mater. Chem. 2005, 15, 2965. (e) El-Safty S. A. et al., Adv. Funt. Mater. 2008, 18, 1739; (f) El-Safty S. A. et al., et al., Adv. Funct. Mater. 2008, 18, 1485; (g) El-Safty S. A. J. Mater. Sci. 2009, 44, 6764].
The immobilization of the indicator chromogen is a crucial step in the preparation of optical chemical sensors for practical applications. The indicator chromogen can be physically immobilized on the support matrixes [Xu H. et al., Anal. Chem., 2001, 73, 4124; Plaschke M. et al., Anal. Chim. Acta, 1995, 304, 107; Clark H. A. et al., Anal. Chem., 1999, 71, 4831; Park E. J. et al., Anal. Chem., 2003, 75, 378] or chemically [Shakhsher M. et al., Anal. Chem., 1990, 62, 1758; Lobnik A. Anal. Chim. Acta, 1998, 367, 159; Ji J. et al., Anal. Chem., 2004, 76, 1411; Munkholm C. et al., Talanta, 1988, 35, 109; Hisamoto H. et al., Anal. Chem., 1998, 70, 1255]. Both of these methodologies have their advantages and disadvantages. Physical entrapment is a simple method, but the sensors prepared will only have a relatively short lifetime because of the leaching of dye molecules into the sample solution [Plaschke M. et al., Anal. Chico. Acta, 1995, 304, 107]. Chemical immobilization by covalent binding of indicator chromogen onto the support matrixes is the most efficient technique for obtaining optical chemical sensors with well reproducible response and long lifetime [Hisamoto H. et al., Anal. Chem., 1998, 70, 1255]. The immobilization process involved in the reaction between indicator chromogens and support matrixes, however, suffers from certain shortcomings such as low limit of detection.
Metal organic frameworks (MOFs) have superior tenability and structural diversity as well as chemical and physical properties. MOFs are extended crystalline coordination polymers built from the combination of multitopic organic linkers and metal—oxo clusters as nodes. The modular, organic and inorganic, nature of these porous materials facilitates chemical manipulations aimed at fine tuning of the structures and functions of metal-organic frameworks to make them suitable for specific applications [Wang Z. et al., Chem. Soc. Rev. 2009, 38, 1315]. Because of their large internal surface areas, extensive porosity, and high degree of crystallinity, MOFs are comparable to traditional porous materials. Studies on the design, synthesis, and characterization of MOFs have been developing rather quickly to explore their promising various applications in magnetism, luminescence, gas adsorption, sensors, and heterogeneous catalysis [De Sa G. F. et al., Coord. Chem. Rev., 2000, 196, 165; Silvio Q. et al., Inorg. Chem., 2004, 43, 1294; Bunzli J. C. G. et al., Chem. Rev., 2002, 102, 1897; Plecnik C. E. et al., Acc. Chem. Res., 2003, 36, 499; El-Shall M. S. et al., Mater. Chem., 2009, 19, 7625; Sun Y. Q. et al., Angew. Chem., Int. Ed., 2005, 44, 5814].
The crystalline nature and the associated structural regularity of MOFs allow exploration of the relationship between structure and various properties. Additionally, molecules confined in a uniform restricted space exhibit unique properties that are not realized in the bulk state. The uniform pore space of MOFs may, therefore, be exploited to conduct chemical reactions or stabilize reaction intermediates.
Unfortunately, preparation of optimal chemosensors useful for detection and removal of HMs still remains highly challenging.
Thus, there remains a need to make new chemosensors and for novel methods to detect and remove heavy metals. The compositions, and methods described herein are directed toward this end.